Retroviral vectors and transposons for stable gene therapy: advances, current challenges and perspectives

Abstract

Gene therapy protocols require robust and long-term gene expression. For two decades, retrovirus family vectors have offered several attractive properties as stable gene-delivery vehicles. These vectors represent a technology with widespread use in basic biology and translational studies that require persistent gene expression for treatment of several monogenic diseases. Immunogenicity and insertional mutagenesis represent the main obstacles to a wider clinical use of these vectors. Efficient and safe non-viral vectors are emerging as a promising alternative and facilitate clinical gene therapy studies. Here, we present an updated review for beginners and expert readers on retro and lentiviruses and the latest generation of transposon vectors (sleeping beauty and piggyBac) used in stable gene transfer and gene therapy clinical trials. We discuss the potential advantages and disadvantages of these systems such as cellular responses (immunogenicity or genome modification of the target cell) following exogenous DNA integration. Additionally, we discuss potential implications of these genome modification tools in gene therapy and other basic and applied science contexts.

Keywords: Clinical trials; Gene therapy; Lentivectors; Transposons.

Fig. 1

Stable gene expression systems. a Representation of simple (e.g. MLV) and complex (e.g. HIV-1) retroviral genomes. b Lentiviral production of 3rd generation vectors and cell transduction. Plasmids containing expression constructs of genetic elements required for packaging (gag-pol, rev and VSV-G, a gene encoding the fusogenic envelope G glycoprotein of the vesicular stomatitis virus) and a plasmid of interest comprised of a chimeric 5′ LTR (long terminal repeat) fused to a heterologous promoter (hP), a promoter (P) to control transgene expression and 3′ Self-inactivating (SIN) LTR are co-transfected together into a producer cell line. After viral production, transduction of lentivector is performed on the target cell. c Cut-and-paste mechanism of SB transposons, where a transposon in a plasmid and a transposase binds to two inverted terminal repeats (ITRs) of the transposon, and precisely cuts the transposon out of the plasmid, inserting the transposon into DNA of the target cell. SB transposons, integrate into TA dinucleotide base pairs, which are duplicated on each end of the insertion site